Separation of 1-butanol from 2-pentanol by extractive distillation

ABSTRACT

1-Butanol is difficult to separate from 2-pentanol by conventional distillation or rectification because of the proximity of their boiling points. 1-Butanol can be easily separated from 2-pentanol by extractive distillation. Effective agents are anisole, ethyl nonanate and butyl ether.

FIELD OF THE INVENTION

This invention relates to a method for separating 1-butanol from 2-pentanol using certain organic compounds as the agent in extractive distillation.

DESCRIPTION OF PRIOR ART

Extractive distillation is the method of separating close boiling compounds from each other by carrying out the distillation in a multiplate rectification column in the presence of an added liquid or liquid mixture, said liquid(s) having a boiling point higher than the compounds being separated. The extractive agent is introduced near the top of the column and flows downward until it reaches the stillpot or reboiler. Its presence on each plate of the rectification column alters the relative volatility of the close boiling compounds in a direction to make the separation on each plate greater and thus require either fewer plates to effect the same separation or make possible a greater degree of separation with the same number of plates. The extractive agent should boil higher than any of the close boiling liquids being separated and not form minimum azeotropes with them. Usually the extractive agent is introduced a few plates from the top of the column to insure that none of the extractive agent is carried over with the lowest boiling component. This usually requires that the extractive agent boil about twenty Celcius degrees or more higher than the highest boiling component.

At the bottom of a continuous column, the less volatile components of the close boiling mixtures and the extractive agent are continuously removed from the column. The usual methods of separation of these two components are the use of another rectification column, cooling and phase separation, or solvent extraction.

The usual method of evaluating the effectiveness of extractive distillation agents is the change in relative volatility of the compounds to be separated. Table 1 shows the degree of separation or purity obtainable by theoretical plates at several relative volatilities. Table 1 shows that a relative volatility of at least 1.2 is required to get an effective separation by rectification.

                  TABLE 1                                                          ______________________________________                                         Effect of Relative Volatility on Theoretical stage                             Requirements.                                                                  Separation Purity,                                                                       Ralative Volatility                                                  Both Products                                                                            1.02    1.1    1.2  1.3  1.4 1.5  2.0  3.0                           (Mole Fraction)                                                                          Theoretical Stages at Total Reflux                                   ______________________________________                                         0.999     697     144    75   52   40  33   19   12                            0.995     534     110    57   39   30  25   14   9                             0.990     463     95     49   34   26  22   12   7                             0.98      392     81     42   29   22  18   10   6                             0.95      296     61     31   21   16  14   8    4                             0.90      221     48     23   16   12  10   5    3                             ______________________________________                                    

1-Butanol and 2-pentanol boil less than a degree apart, have a relative volatility of 1.08 and are impossible to separate by conventional rectification. Table 2 shows that with an agent giving a relative volatility of 1.25, only 56 actual plates are required.

                  TABLE 2                                                          ______________________________________                                         Theoretical And Actual Plates Required vs. Relative                            Volatility For 1-Butanol - 2-Pentanol Separation                               Relative  Theoretical Plates Required                                                                     Actual Plates                                       Volatility                                                                               At Total Reflux, 99% Purity                                                                     Required, 75% Eff.                                  ______________________________________                                         1.20      49               65                                                  1.25      42               56                                                  ______________________________________                                    

OBJECTIVE OF THE INVENTION

The object of this invention is to provide a process or method of extractive distillation that will enhance the relative volatility of 1-butanol from 2,-pentanol in their separation in a rectification column. It is a further object of this invention to identify effective extractive distillation agents that are stable and can be recycled.

SUMMARY OF THE INVENTION

The objects of this invention are provided by a process for the separation of 1-butanol from 2-pentanol which entails the use of certain organic compounds when employed as the agent in extractive distillation.

DETAILED DESCRIPTION OF THE INVENTION

I have discovered that certain organic compounds will effectively increase the relative volatility between 1-butanol and 2-pentanol during rectification when employed as the agent in extractive distillation. They are ethyl benzoate, hexyl formate,propyl butyrate, butyl butyrate, methyl salicylate, ethyl salicylate, ethyl nonanate, 2,6-dimethyl-4-heptanone, 2-undecanone, butyl ether, anisole, acetol, ethanolamine, nitrobenzene and 2,6-dimethylphenol.

                  TABLE 3                                                          ______________________________________                                         Effective Extractive Distillation Agents For                                   Separating 1-Butanol From 2-Pentanol                                                              Relative                                                    Compounds          Volatility                                                  ______________________________________                                         None               1.08                                                        Ethyl benzoate     1.2                                                         Hexyl formate      1.25                                                        Propyl butyrate    1.22*                                                       Butyl butyrate     1.23                                                        Methyl salicylate  1.22                                                        Ethyl salicylate   1.21                                                        Ethyl nonanate     1.25                                                        2,6-Dimethyl-4 heptanone                                                                          1.21                                                        2-Undecanone       1.2                                                         Butyl ether        1.22                                                        Anisole            1.25                                                        Acetol             1.25                                                        Ethanolamine       1.24*                                                       Nitrobenzene       1.21                                                        2,6-Dimethylphenol 1.2                                                         ______________________________________                                          *Reverses the volatility                                                 

THE USEFULNESS OF THE INVENTION

The usefulness or utility of this invention can be demonstrated by referring to the data presented in Tables 1,2 and 3. All of the successful agents show that 1-butanol can be separated from 2-pentanol by means of extractive distillation and that ease of separation is considerable.

WORKING EXAMPLE Example 1

Fifty grams of 1-butanol - 2-pentanol mixture and fifty grams of anisole as the extractive agent were charged to a vapor-liquid equilibrium still and refluxed for three hours. The vapor composition was 80.2% 1-butanol, 19.8% 2-pentanol; the liquid composition was 76.3% 1-butanol and 23.7% 2-pentanol. This is a relative volatility of 1,25. 

I claim:
 1. A method for recovering 1-butanol from 2-pentanol from a mixture consisting of 1-butanol and 2-pentanol which consists essentially of distilling said mixture consisting of 1-butanol and 2-pentanol in the presence of an extractive agent, recovering the 1-butanol as overhead product and obtaining the 2-pentanol and the extractive agent as bottoms product, wherein said extractive agent consists of one material selected from the group consisting of ethyl benzoate, hexyl formate, butyl butyrate, methyl salicylate, ethyl salicylate ethyl nonanate, 2,6-dimethyl- 4-heptanone, 2-undecanone, butyl ether, anisole, acetol, nitrobenzene and 2,6-dimethylphenol.
 2. A method for recovering 2-pentanol from 1-butanol from a mixture consisting of 2-pentanol and 1-butanol which consists essentially of distilling said mixture consisting of 2-pentanol and 1-butanol in the presence of an extractive agent, recovering the 2-pentanol as overhead product and obtaining the 1-butanol and the extractive agent as bottoms product, wherein said extractive agent consists of propyl butyrate or ethanolamine. 